Vocabulary knowledge assessment methods and instruments have gone through a significant evolution. Computer-based tests offer more opportunities than their paper-and-pencil counterparts, however, most digital vocabulary assessments are linear and adaptive solutions in this domain are scarce. The aims of this study were to compare the effectiveness of a multi-stage adaptive and a linear test system of vocabulary knowledge both at test and individual level and to examine the impact of the used assessment method on students' performance and motivation measured through the number of the right answers within a test. Data show that the adaptive test system provided a more accurate ability estimation with higher reliability, a more motivating test environment and more precision than the linear version.